Martial law has been imposed in parts of Songkhla province in southern Thailand.
A series of blasts in Narathiwat knocked out power on Wednesday
The provision covers the two districts of Chana and Thepha, which border three southern provinces already under tight restrictions.
The announcement came as police said three people had been killed in the latest violence in the region, including one man who was beheaded.
About 1,000 people have died in the Muslim-majority south since early 2004.
The army instituted martial law for parts of Songkhla after eight fake explosives were found in Thepha and Chana districts, The Nation newspaper reported.
It is the first time this provision, which allows the authorities to arrest suspects and search their properties without a warrant, has been issued in Songkhla.
Home to most of Thailand's 4% Muslim minority
Muslim rebels fought the government up to the mid-80s
Suspected militants have upped attacks since 2004, targeting Buddhists
Security forces' response criticised by rights groups
The three neighbouring provinces of Yala, Pattani and Narathiwat are all under emergency law, which is not as punitive.
There was violence in all three of these provinces on Wednesday and Thursday, police said.
A man's severed head was found early on Thursday in Talogapo village, Pattani province.
He has not yet been identified as the police have not found the body, but his head was shaved, leading to reports that he was a Buddhist.
Buddhists have frequently been targeted in the insurgency.
Late on Wednesday, a suspected militant blew himself up in Narathiwat town as he set up a device against an electricity pole - one of a series of blasts which knocked out power to the area, police said.
And also on Wednesday, a Muslim villager was shot dead in Raman district of Yala province while riding a motorcycle.
In addition to the fake devices found in Songkhla, there was also a number of fake bombs found in five districts of Pattani province on Thursday, police said.
Effigies of Prime Minister Thaksin Shinawatra were found near these devices, and on roadsides in Yala province.
Those in Yala had Thai national flags across their bodies and the word "Satan" written across their chests.